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Science, Volume 385, Issue 6707, July 2024.

Science, Volume 385, Issue 6707, July 2024.

Science, Volume 385, Issue 6707, July 2024.

Flood occurrence and impact models for socioeconomic applications over Canada and the United States
Manuel Grenier, Mathieu Boudreault, David A. Carozza, Jérémie Boudreault, and Sébastien Raymond
Nat. Hazards Earth Syst. Sci., 24, 2577–2595, https://doi.org/10.5194/nhess-24-2577-2024, 2024
Modelling floods at the street level for large countries like Canada and the United States is difficult and very costly. However, many applications do not necessarily require that level of detail. As a result, we present a flood modelling framework built with artificial intelligence for socioeconomic studies like trend and scenarios analyses. We find for example that an increase of 10 % in average precipitation yields an increase in displaced population of 18 % in Canada and 14 % in the US.

Abstract

Unmodeled errors materially affect the float solutions of both ambiguities and coordinates in global navigation satellite systems (GNSS), and thus also the fixed solution. Recently, extensive attempts have been made to guarantee the reliability of integer ambiguity or reject observation faults for improving the fixed solution in real-time kinematic positioning (RTK), while far too little studies have achieved this by processing the unmodeled errors in long baselines. This contribution is therefore set out to address the unmodeled errors in GNSS RTK long baseline fixed solution. At first, we establish an equation using the quadratic form of the float ambiguity to estimate the float ambiguity bias. Then, based on the estimated float ambiguity bias, a procedure for processing the unmodeled errors in the fixed solution is proposed. Finally, a simulation experiment and a real-measured experiment are conducted, respectively. By applying the proposed procedure, the improvements in the mean and RMSE of the fixed solution bias are found to be approximately 1.11–6.17 cm and 1.06–5.73 cm in three dimensions.

SummaryLarge-scale ocean-bottom node (OBN) arrays of 1000s of multi-component instruments deployed over 1000s of square kilometers have been used successfully for active-source seismic exploration activities including full waveform inversion (FWI) at exploration frequencies above about 2.0 Hz. The analysis of concurrently recorded lower-frequency ambient wavefield data, though, is only just beginning. A key long-term objective of such ambient wavefield analyses is to exploit the sensitivity of sub-2.0 Hz energy to build long-wavelength initial elastic models, thus facilitating FWI applications. However, doing so requires a more detailed understanding of ambient wavefield information recorded on the seafloor, the types, frequency structure and effective source distribution of recorded surface-wave modes, the near-seafloor elastic model structure, and the sensitivity of recorded wave modes to subsurface model structure. To this end, we present a wavefield analysis of low- and ultra-low-frequency ambient data (defined as <1.0 Hz and <0.1 Hz, respectively) acquired on 2712 OBN stations in the Amendment Phase 1 survey covering 2750 km2 of the Gulf of Mexico. After applying ambient data conditioning prior to cross-correlation and seismic cross-coherence interferometry workflows, we demonstrate that the resulting virtual shot gather (VSG) volumes contain evidence for surface-wave and guided P-wave mode propagation between the 0.01-1.0 Hz that remains coherent to distances of at least 80 km. Evidence for surface-wave scattering from near-surface salt-body structure between 0.35-0.85 Hz is also present in a wide spatial distribution of VSG data. Finally, the interferometric VSG volumes clearly show waveform repetition at 20 s intervals in sub-0.3 Hz surface-wave arrivals, a periodicity consistent with the mean active-source shot interval. This suggests that the dominant contribution of surface-wave energy acquired in this VSG frequency band is likely predominantly related to air-gun excitation rather than by naturally occurring energy sources. Overall, these observations may have important consequences for the early stages of initial model building for elastic FWI analysis.

SummaryEarth’s plate tectonic behavior arises from lithospheric ductile weakening and shear-localization. The ubiquity of mylonites at lithospheric shear zones is evidence that localization is caused by mineral grain-size reduction. Most lithospheric mylonites are polymineralic, suggesting that the interaction between mineral phases by Zener pinning promotes grain-size reduction and weakening. Yet this interaction only occurs where mineral phases mix at the grain scale. Phase mixing and its effect on microstructure and strength have been shown in deformation experiments and natural field samples. Our theory for the interaction between phase mixing (treated as a stress driven diffusion) with two-phase grain damage has been compared to lab experiments. But using processes at the tiny grain-scale embedded within the small hand-sample and lab scales to model large-scale lithospheric processes, requires an upscaling scheme that captures the physics from micro- to macro-structures. For example, weakening from grain-damage in zones of mixing can lead to banded viscosity structure at the small scale that manifests as viscous anisotropy at the large scale. Here we provide a new framework for self-consistently upscaling from microscopic (grain) scales, to mesoscopic (petrological heterogeneity) scales to macroscopic (tectonic) scales. The first upscaling step models phase mixing and grain-size evolution in a small “mesoscopic” lab-scale volume or “patch”, which is equivalent to a point in the macroscopic space. Within this mesoscale patch, stress driven diffusive mixing is described by an analytical solution for mineral phase fraction, provided a minimalist Fourier representation of phase fraction, and a transformation to the patch frame of reference as well as to the principal stress directions at that point. The orientation and volume fraction of mixed-phase regions can then be extracted from the analytical solution for phase fraction. The grain-size and viscosity in the mixed bands are determined by two-phase grain-damage theory; the unmixed zone properties follow from mono-phase grain damage theory. The mesoscale banded viscosity field leads to a macroscale anisotropic viscosity at that point in space. But, the evolution of properties at each macroscale point involves tracking only a few quantities (phase fraction, grain sizes) rather than modeling each patch of mesoscale space as its own 2-D or 3-D system. For the final upscaling, the anisotropic viscosity field is used in a macroscale lithosphere flow model. We show an example of this scheme for a lithospheric Rayleigh-Taylor drip driven by ridge-push compressive stress, which can cause anisotropic weakening via grain mixing and damage that may help initiate subduction and passive margin collapse.

SummaryThe crust of the South American platform recorded imprints of dynamic processes related with the opening of the Central and South Atlantic but has not been well measured. Crustal structure can be retrieved from teleseismic receiver functions using H-κ stacking, but nearly-parallel stripes of high stacking values existing in stacking images for seismic stations in sedimentary area cause difficulties in identifying solutions. We show that some seemingly spurious stripes that do not point to any layer solution are helpful in the identification of the solution position. With the aid of the auxiliary stripes, we retrieved thicknesses and Vp/Vs of sedimentary and crystalline crust for 65 permanent stations of the Brazilian Seismographic Network and 6 new portable seismic stations in Brazil and Uruguay. The resulted sedimentary thickness and Vp/Vs exhibit a good correlation with the Phanerozoic sediments in the South American basins. The crust of Paraná–Etendeka Large Igneous Province (LIP) had been expected to be more mafic since it had ever been penetrated by mantle magma in the Cretaceous related to the south Atlantic opening. However, we found very low Vp/Vs (1.67) in the crystalline crust beneath the LIP, implying a more felsic crust and that no significant mafic intruding/underplating has occurred in the region. The more felsic crust may be formed in a special evolution early than the magmatic event, or during the magmatic event by releasing crustal volatiles. The resulted sedimentary thickness and Vp/Vs ratios exhibit a good correlation with the Phanerozoic sediments in the South American basins, which implies that Triassic–Jurassic and Cretaceous magmatism did not cause significant metamorphism in sediments formed before the magmatic events.

Abstract

The quality factor Q is a dimensionless measure of the energy loss per cycle of a wave field, and a proper understanding of this factor is important in a variety of fields, from seismology, geophysical prospecting to electrical science. Here, the focus is on viscoelasticity. When interpreting experimental values, several factors must be taken into account, in particular the shape of the medium (rods, bars or unbounded media) and the fact that the measurements are made on stationary or propagating modes. From a theoretical point of view, the expressions of Q may differ due to different definitions, the spatial dimension and the inhomogeneity of the wave, i.e. the fact that the vectors of propagation (or wavenumber) and attenuation do not point in the same direction. We show the difference between temporal and spatial Q, the relationships between compressional and shear Q, the dependence on frequency, the case of poro-viscoelasticity and anisotropy, the effect of inhomogeneous waves and various loss mechanisms, and consider the analogy between elastic and electromagnetic waves. We discuss physical theories describing relaxation peaks, bounds on Q and experiments showing the behaviour of Q as a function of frequency, saturation and pore pressure. Finally, we propose an application example where Q can be used to estimate porosity and saturation.

Abstract

We present measurements of 30–700 keV Solar Energetic Electrons (SEEs) near the Moon when within the terrestrial magnetotail by the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun spacecraft. Despite their detection deep within the tail, the incident flux and spectral shape of these electrons are nearly identical to measurements taken upstream of Earth in the solar wind by the Wind spacecraft; however, their pitch angle distribution is isotropized compared to the more field-aligned distribution upstream. We illustrate that SEEs initially traveling Earthward precipitate onto the lunar far-side, generating extended shadows in the cis-lunar electron distribution. By modeling the dynamics of these electrons, we show that their precipitation patterns on the lunar near-side are comparatively reduced. The non-uniform precipitation and accessibility of potentially hazardous electrons to the Moon's surface are highly relevant in the context of astronaut safety during the planned exploration of the lunar environment.

Scientists have known from ice core research that it's easier to melt an ice sheet than to freeze it up again. Now, they know at least part of the reason why, and it has to do with ice's "sponginess," according to a new study published July 24 in The Cryosphere.

Abstract

Subsurface gas storage is crucial for achieving a sustainable energy future, as it helps to reduce CO2 emissions and facilitates the provision of renewable energy sources. The confinement effect of the nanopores in caprock induces distinctive thermophysical properties and fluid dynamics. In this paper, we present a multi-scale study to characterize the subsurface transport of CO2, CH4, and H2. A nanoscale-extended volume-translated Cubic-Plus-Association equation of state was developed and incorporated in a field-scale numerical simulation, based on a full reservoir-caprock suite model. Results suggest that in the transition from nanoscale to bulk-scale, gas solubility in water decreases while phase density and interfacial tension increase. For the first time, a power law relationship was identified between the capillary pressure within nanopores and the pore size. Controlled by buoyancy, viscous force and capillary pressure, gases transport vertically and horizontally in reservoir and caprock. H2 has the maximum potential to move upward and the lowest areal sweep efficiency; in short term, CH4 is more prone to upward migration compared to CO2, while in long term, CH4 and CO2 perform comparably. Thicker caprock and larger caprock pore size generally bring greater upward inclination. Gases penetrate the caprock when CH4 is stored with a caprock thickness smaller than 28 m or H2 is stored with a caprock pore size of 2–10 nm or larger than 100 nm. This study sheds light on the fluid properties and dynamics in nanoconfined environment and is expected to contribute to the safe implementation of gigatonne scale subsurface gas storage.

Abstract

Bottom currents play a major role in deep-sea sedimentation, but their significance in the burial of organic carbon is poorly quantified at a global scale. Here we show that Holocene fluxes of organic carbon into the contourite drifts are high, with a global average of 0.09 g cm−2 Kyr−1. At individual drift sites, fluxes are commonly 1–2 orders of magnitude greater than rates in surrounding areas and in global depth-similar zones. These high fluxes of organic carbon into the contourite drifts are due to high rates of sedimentation. Over the past 50 million years, sedimentation rates at the studied contourite drift sites have overall increased, coincident with decreasing atmospheric CO2 and a cooling global climate. Our work suggests that a ramp-up of the bottom-current carbon pump has accelerated removal of CO2 from the atmosphere and oceanic water, thus contributing to the overall global cooling after the Eocene Thermal Maximum.

Abstract

Complex natural fracture networks typically consist of multiple clusters, whose connectivity is rarely quantified. Therefore, for each identified fracture network, we propose a connectivity metric that accounts for individual fracture clusters and their interactions. This metric evaluates contributions from all fracture clusters, considering their relative sizes and interactions among the isolated clusters, which in turn depend on the hydraulic conductance of the interconnecting rock matrix. Furthermore, we investigate how the system connectivity depends on fracture sealing, alterations of central clusters, and cluster linkage. Fracture sealing strongly impacts overall fracture connectivity, with 5 percent of sealed fractures reducing connectivity by 20 percent. The connectivity reduction is small when transitioning the central cluster from the largest to the smallest one. However, the largest cluster significantly contributes to overall connectivity, while the smallest one contributes minimally. Natural fracture networks increase connectivity by linking more clusters, with heterogeneity and anisotropy playing pivotal roles.

What can we learn from global disaster records about multi-hazards and their risk dynamics?
Wiebke S. Jäger, Marleen C. de Ruiter, Timothy Tiggeloven, and Philip J. Ward
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-134,2024
Preprint under review for NHESS (discussion: open, 0 comments)
Multiple hazards, occurring at the same time or shortly after one another, can have more extreme impacts than single hazards. We examined the disaster records in the global emergency events database EM-DAT to better understand this phenomenon. We developed a method to identify such multi-hazards and analyzed their reported impacts using statistics. Multi-hazards have accounted for a disproportionate amount of the overall impacts, but there are different patterns in which the impacts compound.

Abstract

Since the 1950s, observations and climate models show an amplification of sea surface temperature (SST) seasonal cycle in response to global warming over most of the global oceans except for the Southern Ocean (SO), however the cause remains poorly understood. In this study, we analyzed observations, ocean reanalysis, and a set of historical and abruptly quadrupled CO2 simulations from the Coupled Model Intercomparison Project Phase 6 archive and found that the weakened SST seasonal cycle over the SO could be mainly attributed to the intensification of summertime westerly winds. Under the historical warming, the intensification of summertime westerly winds over the SO effectively deepens ocean mixed layer and damps surface warming, but this effect is considerably weaker in winter, thus weakening the SST seasonal cycle. This wind-driven mechanism is further supported by our targeted coupled model experiments with the wind intensification effects being removed.

Abstract

Solar-induced fluorescence (SIF) is a proxy of ecosystem photosynthesis that often scales linearly with gross primary productivity (GPP) at the canopy scale. However, the mechanistic relationship between GPP and SIF is still uncertain, especially at smaller temporal and spatial scales. We deployed a ultra-hyperspectral imager over two grassland sites in California throughout a soil moisture dry down. The imager has high spatial resolution that limits mixed pixels, enabling differentiation between plants and leaves within one scene. We find that imager SIF correlates well with diurnal changes in leaf-level physiology and gross primary productivity under well-watered conditions. These relationships deteriorate throughout the dry down event. Our results demonstrate an advancement in SIF imaging with new possibilities in remotely sensing plant canopies from the leaf to the ecosystem. These data can be used to resolve outstanding questions regarding SIF's meaning and usefulness in terrestrial ecosystem monitoring.

Abstract

This study investigates the potential impact of Solar Energetic Particles (SEPs) on the V0 layer of the Venus ionosphere. Electron density profiles obtained from radio occultation experiments conducted by the Venus Express (VEX) and Akatsuki missions were utilized for this purpose. Background data from the Analyzer of Space Plasma and EneRgetic Atoms (ASPERA-4) aboard VEX were used to detect SEP events. Additionally, observations from the Space Environment Monitor (SEM) suite onboard the Geostationary Operational Environmental Satellite (GOES) during alignments of Venus, Earth, and the Sun were also considered. Our findings indicate that while SEPs may contribute to the formation of the V0 layer, they are not the main driving force in the Venusian ionosphere.

A type of invisible, unpredictable air turbulence is expected to occur more frequently in the Northern Hemisphere as the climate warms, according to new research. Known as clear air turbulence, the phenomenon also increased in the Northern Hemisphere between 1980 and 2021, the study found.

Rainfall fluctuates more vigorously. Why? Scientists say it's because of us. Many people around the world have noticed that rainfall is becoming increasingly erratic. Intense downpours are occurring more frequently, while dry periods seem to last longer and become more severe. These changes have raised concerns and prompted scientists to investigate the links between climate change and these unpredictable rainfall patterns.